HTMLy is an open source databaseless blogging platform. The Flat-File Blog and Flat-File CMS written in PHP.
Mara CMS performs a similar core function to 'Content management systems' like Drupal or Wordpress - although it differs in many fundamental aspects from those packages. Probably the most significant difference is its being file based instead of database dependent.
Monstra is a modern and lightweight Content Management System. It is Easy to install, upgrade and use.
Nibbleblog is a powerful engine for creating blogs, all you need is PHP to work.
PhileCMS is a file-driven CMS. Powered By Markdown And Twig. But You Can Change That.
Pulse CMS is the easiest way to build and deploy a responsive, content managed website.
Singularity is a simple (single PHP file), flat file CMS which marks up HTML using Markdown.